Arc coil spring configuration

ABSTRACT

Improved performance of arc coil springs by stress reduction when they are bottomed out is achieved by forming the coil spring wire in a substantially trapezoidal or other shape such that when bottomed, the side surfaces of the coil abut and carry the bottoming load which is distributed over a comparatively large surface area. The angles of the sidewalls of the substantially trapezoidal cross section wire are preferably coincident with lines of radius when the spring is installed in an arc in a clutch, damper or flywheel. The radius of the outer surface of the arc coil spring wire is matched to the radius of the inner surface of the guide or housing so that the area of contact is large, thereby distributing the outwardly directed spring force over a large area, reducing the force per unit area and improving lubrication retention on the contacting surfaces.

FIELD

The present disclosure relates to coil springs utilized in arc (curved)applications and more particularly to coil springs utilized in arcapplications having a coil cross section that minimizes wear and stressassociated with bottoming.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may or may not constitute priorart.

Coil compression springs find wide application as energy storage devicesin power train components where they temporarily absorb drivelinetransients and smooth power delivery. They are frequent and commoncomponents of manual transmission clutches, disposed between drive anddriven components where they lessen driveline shock and smooth clutchengagement.

In such applications, the coil spring is frequently installed not in astraight line, helical configuration but in an arc, its radius ofcurvature dictated by its distance from the center axis (of rotation) ofthe clutch. The installation of a coil compression spring in an arccreates a plethora of engineering, design and service issues.

For example, whereas the bottoming of a conventional straight helicalcoil spring occurs essentially everywhere along a helical line ofcontact between adjacent coils, bottoming of an arc coil spring occursonly proximate its inner diameter in the region where the coils arecloser in its uncompressed state. In fact, only a very small region ofeach coil may carry the bottoming load. Thus, coils of an arc coilspring are subjected to higher stress for the same bottoming loadrelative to a straight helical spring since only a portion of each coilcarries the load.

Another engineering issue relates to the outer surface of an arc coilspring. Almost without exception, an arc coil spring is constrainedwithin a guide or housing which maintains the spring in its properposition between end points. Specifically, it is the outer surface ofthe arc coil spring that must be constrained and this is generallyaccomplished by a curved housing that at least partially surrounds thearc spring. Accordingly, there will typically be significant force andfriction between the outer surface of the arc spring and the innersurface of the curved spring housing.

The present invention is directed to solving these problems andimproving the performance and service life of arc coil springs.

SUMMARY

The present invention provides an arc coil spring having improvedperformance and service life. To improve the performance of an arc coilspring by reducing stress when it is bottomed, the cross section of thewire from which the coil is fabricated is substantially trapezoidal suchthat when bottomed, the angled flat sidewalls of the coils abut andcarry the bottoming load which is distributed over a comparatively largesurface area. From a spacial geometry standpoint, the contact betweenadjacent coils is along a line of radius rather than the point contactbetween adjacent coils of a round wire, prior art spring. The angle ofthe sidewalls of the trapezoidal cross section wire is selected so thatwhen the spring is disposed in an arc, the angled sidewalls of the innercoils of the spring are coincident with lines of radius. It will beappreciated that alternate embodiment sidewall configurations such ascomplementary oblique or complementary concave and convex surfaces whichabut along a line of contact when the spring is fully compressed orbottomed out are within the purview of this invention.

Additionally, the radius of the outer surfaces of the coils of the arccoil spring coincides with the radius of the inner surface of the guideor housing containing the arc spring so that the area of contact islarge, thereby distributing the outwardly directed spring force over arelatively large area, reducing the force per unit area and improvinglubrication retention on the contacting surfaces.

Thus it is an aspect of the present invention to provide an arccompression spring having a coil wire cross section that issubstantially trapezoidal.

It is a further aspect of the present invention to provide an arc coilspring having coil wire having parallel contacting sidewalls when thespring is bottomed out.

It is a still further aspect of the present invention to provide an arccoil spring having coil wire having sidewalls which abut along a line ofradial contact when the spring is bottomed out.

It is a still further aspect of the present invention to provide an arccoil spring having coil wire having radial and oblique sidewalls orconcave and convex sidewalls.

It is a still further aspect of the present invention to provide an arccoil spring having coil wire having a radiused outer surface thatconforms to the radius of the inner surface of a housing.

It is a still further aspect of the present invention to provide an arccoil spring having improved stress carrying capability when bottomedout.

It is a still further aspect of the present invention to provide an arccoil spring having improved lubrication and reduced friction between thespring and a housing.

Further aspects, advantages and areas of applicability will becomeapparent from the description provided herein. It should be understoodthat the description and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of the presentdisclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a front, elevational view of a dual mass flywheelincorporating arc coil springs according to the present invention;

FIG. 2 is an enlarged, fragmentary, sectional view of a plurality offully compressed, i.e., bottomed out, coils of an arc coil spring of adual mass flywheel according to the present invention;

FIG. 3 is a greatly enlarged, cross sectional view of an outer coil wireof an arc coil spring according to the present invention;

FIG. 4 is an enlarged, fragmentary, sectional view of a coil of a firstalternate embodiment of an arc coil spring according to the presentinvention; and

FIG. 5 is an enlarged, fragmentary, sectional view of a coil of a secondalternate embodiment of an arc coil spring according to the presentinvention.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses.

With reference to FIG. 1, a portion of a rotating transient absorbingand damping device such as a clutch, damper or dual mass flywheelincorporating the present invention is illustrated and generallydesignated by the reference number 10. The dual mass flywheel 10includes a first circular plate or disc 12 axially spaced from a secondcircular plate or disc 22. Each of the plates or discs 12 and 22 areconnected to respective co-axial drive and driven members such as shaftsor quills (both not illustrated) and define a curved spring receivingpassageway or opening 14 having lugs, tabs or stops 16 and 26 atopposite ends on opposite plates or discs 12 and 22 that apply force toa pair of diametrically opposed arc coil springs 30 and locate theirends. That is, at one end of the coil spring 30 in the upper portion ofFIG. 1, for example, the left end, the first plate or disc 12 includes alug, tab or stop 16 that engages the arc coil spring 30 and at the otherend, the right end, the second plate or disc 22 includes a lug, tab orstop 26 that engages the arc coil spring 30.

A second set of the lugs, tabs or stops 16 and 26 engage the ends of thearc coil spring 30 in the lower portion of FIG. 1. Preferably, the endsof the arc coil springs 30 are ground so that the end surface is smooth,flat and essentially perpendicular to the axis of the arc coil spring 30when it is in a relaxed, .i.e., straight, state. The two arc coilsprings 30 thus cooperatively act as a damper or transient shockabsorber between the drive and driven members connected to the plates ordiscs 12 and 22. Each of the arc coil springs 30 includes a plurality ofcoils 32 which extend in an arc over slightly less than 180° when in arelaxed state as illustrated in FIG. 1. It should be appreciated thatmore arc coil springs 30 each extending over smaller circumferentialarcs or angles may also be utilized with the present invention. Forexample, three arc coil springs 30 each extending over slightly lessthan 120° or four arc coil springs 30 each extending over slightly lessthan 90° may alternatively be utilized with the present invention. Oneor both of the circular plates or discs 12 and 22 includes all orportions of a curved circular housing, surface or guide 34 which retainsthe arc coil springs 30 in position between the lugs or tabs 16 and 26and against which the outer surfaces of the arc coil springs 30 are incontact, slide against and are restrained.

Referring now to FIG. 2, a portion of the upper one of the arc coilsprings 30 illustrated in FIG. 1 is illustrated in a compressed,bottomed out state, that is, in the inner portion 36 of the arc spring30, the inner coils 32 are compressed against one another due to a hightorque differential across the driven and driven plates or discs 12 and22 of the dual mass flywheel 10 such that no further relative rotarymotion (in the direction of spring compression) between the drive anddriven plates or discs 12 and 22 is possible. Stated somewhatdifferently, the arc coil springs 30 bottom out when the computed orrequired angular compression of the arc coil springs 30 is equal to orgreater than the applied torque divided by the spring constant of thetwo arc coils springs 30.

Certain consequences follow from this fully compressed condition. Firstof all, the arc coil springs 30 cease to provide any damping or shockabsorbing and any rotational transients or shocks will be transmittedessentially without modification through the damper or dual massflywheel 10. Second of all, instead of being transmitted helicallythrough the entire length of the coils of the arc coil springs 30, thetorque will be transmitted from side face to side face or surface tosurface 38 through the inner coils 36 of the arc coil springs 30. Thus,the side faces or surfaces 38 of the inner coils 36 may be subjected tohigh constant or repeated transient stress.

As illustrated in FIG. 2, the adjacent side faces or surfaces 38 of theinner coils 36 of the arc coils springs 30 are formed or shaped todefine, i.e., be co-planar with, lines of radius or reference planes R1which are perpendicular to the plane of the drawing when in either acurved, relaxed state, as illustrated in FIG. 1 or in a fully compressed(bottomed out) state as illustrated in FIG. 2. Thus, along a radial lineand for at least a small portion of their circumference, the side facesor surfaces 38 of adjacent inner coils 36 of the arc spring 30 are inflat, intimate contact with one another. The smaller the mean diameterof the inner coils 36 (and the arc coil spring 30 overall) and thesmaller their number over a given arc or circumferential angle, thelarger is the included angle between the side faces or surfaces 38 of asingle coil. The larger the mean diameter of the inner coils 36 (and thearc coil spring 30 overall) and the greater their number over a givenarc or circumferential angle, the smaller is the included angle betweenthe side faces or surfaces 38 of a single coil.

The included angle between the side faces or surfaces 38 of an innercoil 36 may be readily calculated if the number of coils in a fullycompressed or bottomed out state and the included circumferential angleof the bottomed out inner coils 36 are known. For example, if thirteenbottomed out inner coils 36 occupy an angle of 90°, each inner coil 36will occupy 6.92° and thus for the two side faces or surfaces 38 tocoincide with lines of radius, the included angle between the side facesor surfaces 38 will be 6.92° and each side face or surface 38 will be atan angle of 3.46° to a line of radius. Functional included anglesbetween the side faces or surfaces 38 of the spring wire 40 will rangefrom less than 2° to about 10°. The cross section of the spring wire 40of the coils of the arc spring 30 in the preferred embodiment is thussubstantially trapezoidal. It should be appreciated that thesubstantially trapezoidal, nearly square, cross section of the springwire 40 of the arc coil spring 30 in general allows higher energydensity than conventional, round spring wire due to the r/J strainrelationship in bending because more material is at a greater distancefrom the centerline of the arc coil spring 30.

Referring now to FIGS. 2 and 3, it should be appreciated that given thesubstantially trapezoidal cross section of the spring wire 40 and thefact that such arc coil springs 30 are wound from such trapezoidal crosssection wire 40, having the side faces or surfaces 38 of the inner coils36 defining lines or planes that converge at the center axis of the dualmass flywheel 10 means that the outer coils 42 with the same side facesor surfaces 38 will define lines or planes that converge radiallyoutwardly. As illustrated in FIG. 2, this configuration places narrow(inner) edges of the faces or surfaces 38 of the outer coils 42proximate one another in direct opposition to the present teaching. Thisconfiguration and arrangement is of no consequence, however, as theouter coils 42 of the arc coil spring 30 are incapable of having theiradjacent faces or surfaces 38 contact one another, i.e., bottom out,when disposed in an arc as illustrated in FIG. 1 or so disposed andbottomed out as illustrated in FIG. 2.

The outer face or surface 46 of the spring wire 40 and thus of the outercoils 42 defines a curve or radius R2 essentially equal to the radius ofthe inner surface or guide 34 (illustrated in FIG. 1). Thus, as the arccoil spring 30 circumferentially compresses within the circular housing,surface or guide 34, friction is reduced and smooth motion isfacilitated due to the complementary radiused surfaces: the outer faceor surface 46 of the spring wire 40 and the surface or guide 34. Thisconfiguration increases the area of contact, thereby distributing theoutwardly directed force of the arc spring 30 over a large area,reducing the force per unit area and improving lubrication retention onthe contacting surfaces 34 and 46. The inside face or surface 48 of thespring wire 40 may be flat and at equal angles to the side faces 38 andthus parallel to the axis of the spring 30 in a relaxed, i.e., straight,state or any other readily achieved configuration and finish as it doesnot contact other surfaces or elements or contribute to the improvedfunction of the invention.

Referring now to FIGS. 4 and 5, it will thus be appreciated that thecentral feature of an arc coil spring according to the present inventionis the configuration of the sidewalls or side faces 38 of the arc spring30 such that they are parallel and in contact along a line of radius andcircumferentially as well over a small distance, thereby avoiding theessentially point contact which an arc spring fabricated of conventionalround spring wire is subjected to when disposed in an arc and bottomedout. Accordingly, it should be understood that sidewall profiles otherthan flat and coincident with a line of radius when disposed in a givenarc may be utilized. For example, in FIG. 4, an arc spring 50 isillustrated having sidewalls 52A and 52B disposed at significant anglesthat nonetheless result in line contact between adjacent sidewalls 52Aand 52B when the arc spring 50 is fully compressed or bottomed out.Other sidewall angles and profiles, such as radiused, i.e., mating ornesting concave and convex curved surfaces 58A and 58B on an arc coilspring 60 as illustrated in FIG. 5, are also deemed to be within thepurview of the present invention. Both embodiments 50 and 60 include theouter radiused face or surface 46 which is complementary to the surfaceor guide 34 (illustrated in FIG. 1).

The description of the invention is merely exemplary in nature andvariations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. An arc spring and housing for a rotating damper comprising, incombination, a housing having a region for receiving an arc spring, saidregion having an outer, curved, spring engaged surface defining a radiusand a stop at each end of said spring receiving region, and an arcspring disposed in said region between said stops, said arc springdefining a plurality of coils, said coils fabricated of spring wirehaving sidewalls configured to contact one another along a line whenfully compressed and an outer surface of said spring wire having aradius of curvature substantially equal to said radius of said curved,spring engaged surface of said housing.
 2. The arc spring and housing ofclaim 1 wherein a cross section of said spring wire is trapezoidal andsaid sidewalls are disposed at angles conforming to lines of radius whensaid plurality of coils are disposed in said housing.
 3. The arc springand housing of claim 1 wherein said housing includes a first driveportion and a second driven portion and wherein one of said stops iscoupled to said first drive portion and another of said stops is coupledto said second driven portion.
 4. The arc spring and housing of claim 1wherein said sidewalls of said spring wire are one of converging,oblique and complementarily curved.
 5. The arc spring and housing ofclaim 1 wherein inner regions of said arc spring are in sidewall tosidewall contact when said arc spring is fully compressed.
 6. The arcspring and housing of claim 1 wherein said sidewalls of said coilsconverge at an angle between approximately 2° and 10°.
 7. The arc springand housing of claim 1 wherein a pair of arc springs are disposed insaid housing in diametrical opposition.
 8. The arc spring and housing ofclaim 1 wherein angles between said sidewalls increase when a radius ofcurvature of said arc spring decreases and when said circumferentialwidth of said spring wire increases.
 9. A coil spring for incorporationin a rotating transient absorber, comprising, in combination, aplurality of helical coils of spring wire, said coils spaced apart in arelaxed state, said spring wire defining a substantially trapezoidalcross section having opposed sidewalls defining planes converging awayfrom said spring and an outer radiused surface extending between saidsidewalls.
 10. The coil spring of claim 9 wherein said coils are spacedapart along an axis and said spring wire is wider closer to said axisand narrower farther from said axis.
 11. The coil spring of claim 10wherein a surface of said coils closest to said axis is substantiallyparallel to said axis.
 12. The coil spring of claim 9 wherein saidopposed sidewalls define angles between approximately 2° and 10°. 13.The coil spring of claim 9 wherein said outer radiused surface defines aradius equal to a radius of a spring housing of such rotating transientabsorber.
 14. The coil spring of claim 9 wherein said coil spring isdisposed in an arc, in at least diametrically opposed pairs in suchrotating transient absorber.
 15. A flywheel assembly comprising, incombination, a first flywheel disc having at least one first spring stopand at least a portion of a circumferential spring housing having afirst inner surface of a first radius of curvature, a second flywheeldisc having a least a second spring stop, an arc compression springdisposed between said first and said second spring stops and within saidportions of said housing, said arc compression spring having coil wiredefining a substantially trapezoidal cross section, said trapezoidalcross section having converging sidewalls conforming to lines of radiusand a narrower end of said trapezoidal cross section having a secondradius of curvature substantially equal to a said first radius ofcurvature of said first inner surface of said spring housing.
 16. Theflywheel assembly of claim 15 wherein said flywheel is a dual massflywheel.
 17. The flywheel assembly of claim 15 wherein said firstflywheel disc includes a first drive portion and said second flywheeldisc includes a second driven portion.
 18. The flywheel assembly ofclaim 15 wherein inner regions of said arc compression spring are insidewall to sidewall contact when said arc compression spring is fullycompressed.
 19. The flywheel assembly of claim 15 wherein said first andsecond flywheel discs include a plurality of stops and a plurality ofsaid arc compression springs are disposed between said stops.
 20. Theflywheel assembly of claim 15 wherein said converging sidewalls defineangles between approximately 2° and 10°.